Robinia pseudoacacia L.—Black locust
FAMILY: Fabaceae (Leguminosae)—the Bean Family (see Crota/aria)
PHENOLOGY: Long, fragrant, white, grapelike clusters of flowers are produced in May and June.
DISTRIBUTION: Robinia pseudoacacia is a native tree inhabiting woods, thickets, and fencerows.
PLANT CHARACTERISTICS: Black locust is an open tree that can reach a height of 25 m; stipules: modified into two opposing spines 1 cm long flankingthe base of the petiole; leaves: odd pinnately compound; leaflets: up to 9 pairs, elliptic to ovate-obtuse, 2-4 cm; inflorescence: a raceme, dense, drooping, many-flowered, 20 cm long; flowers: white. fragrant, 2-2.5 cm; fruit: 5-10 cm long, reddish brown, glabrous, remaining in clusters on the tree over winter and becoming black.
POISONOUS PARTS: Toxins are produced by the plant and accumulate in the leaves, seeds, and inner bark. In controlled experiments on horses an aqueous extract of bark (0.1% of body weight) and powdered bark (0.04% of the body weight) were found toxic. Poisonous principles are about one-tenth as toxic to cattle.
SYMPTOMS: Toxic reactions include weakness, depression, anorexia, vomiting, diarrhea (blood may be present), nausea, dilated pupils, coldness of extremities, and weak and irregular pulse. Lesions include irritation and edema of the digestive mucosa and severe gastroenteritis. There may be venous congestion. Also, a yellowish pigmentation of the membranes, similar to icterus, may be present. Fatalities are rare.
POISONOUS PRINCIPLES: Two compounds are suspected to be involved in toxicity, a heat-labile phytotoxin, robin, and the glycoside robitin. Additional isolated compounds include acetin and robinetin; it is uncertain what role these substances play in toxicosis.
CONFUSED TAXA: Two other species of Robinia are found in Pennsylvania: R. hispida L. and R. viscosa Vent. Both species have pink flowers and seed pods with stiff spreading hairs, The honey locust, G]editsia triacanthos L., a tall tree with branched thorns, has more narrow (oblonglanceolate) leaflets that are obscurely crenate. The leaves of this plant are even-pinnate or bipinnate and the flowers unisexual. Honey locust seed pulp is considered to be a pleasant tasting, sweet nibble but should not be confused with the poisonous pulp of Kentucky coffeetree (see Gymnociadus).
SPECIES OF ANIMALS AFFECTED: Humans and a wide variety of livestock have shown symptoms. These include horses, cattle, sheep, and poultry.
TREATMENT: (11a)(b); (26); (13)
OF INTEREST: This plant is listed in some texts as an emergency-food: inner bark, flowers fried or infused in water for a beverage. Extreme caution should be exercised in this regard. Other species may be toxic. Clammy locust (rose-acacia), R. viscosa Vent., a native in mountain woods, and bristly locust (also called rose-acacia), R. hispida L. ~ a roadside and spoil-bank taxon, may be poisonous.